Autopilot operation

[Bill3558]

2008 CTLS.  Trutrac autopilot.  Roll control is good, but pitch is not. It seems to hunt nose down then nose up. I have to add and reduce power to avoid overspeed and too slow speed. Is this the nature of the beast?  
Appreciate any thoughts. I don’t know if it’s broken or not. 
Curious to know when you guys use the autopilot.  I find it not good in turbulence. It seems to be way behind the airplane. 

[Roger Lee]

It may just need the sensitivity set better in the menu.

Bad turbulence is usually better hand flown vs the AP.

[Bill3558]

It never occurred to me to read the instruction manual, lol.  I’ll check that. 

[John Vance]

In turbulence the AP does its best to hold altitude. In an updraft it will nose down, your airspeed will increase, and engine speed will increase with it.  Obviously the opposite occurs with a downdraft.  So with AP on, you need to keep a hand on the throttle.  Or fly by hand and let your altitude vary a bit. 

[John Vance]

In turbulence the AP does its best to hold altitude. In an updraft it will nose down, your airspeed will increase, and engine speed will increase with it.  Obviously the opposite occurs with a downdraft.  So with AP on, you need to keep a hand on the throttle.  Or fly by hand and let your altitude vary a bit. 

[Bill3558]

Thanks gents.  I adjusted the vertical sped from 6 to 3 in the autopilot settings and that seems to have fixed it. 

[Animosity2k]

Great info! I always wondered this same thing. I'm always playing with the throttle and the electric trim . 

[FlyingMonkey]

There is a limit to how well the AP can handle turbulence.  In anything but calm air you will constantly have to make small throttle adjustments.  In really bumpy conditions you may be making pretty big throttle swings.  At some point it just becomes easier to hand fly it.  In light chop the AP can reduce workload, in heavy chop it just adds stress to the pilot.

Look at sensitivity and gain settings.  Those are usually the culprits for hunting issues.  Check gain first.

[Tom Baker]

Whether you are hand flying or using the autopilot if you try to maintain altitude while it is bumpy the RPM will change. Altitude is relative to the ground, but the airplane is flying in an airmass. When it gets bumpy the airmass is moving up and down. If the airmass is moving up and you try to maintain altitude it is like putting the airplane in a dive with calm conditions. The opposite happens when the airmass is going down. RPM will change with an airplane that has a direct drive engine, but the change is amplified by 2.43 with the Rotax power. Unless you are running where the RPM goes above 5500 I would just let it change, otherwise you will be constantly chasing it.

[FlyingMonkey]

3 minutes ago, Tom Baker said:

Whether you are hand flying or using the autopilot if you try to maintain altitude while it is bumpy the RPM will change. Altitude is relative to the ground, but the airplane is flying in an airmass. When it gets bumpy the airmass is moving up and down. If the airmass is moving up and you try to maintain altitude it is like putting the airplane in a dive with calm conditions. The opposite happens when the airmass is going down. RPM will change with an airplane that has a direct drive engine, but the change is amplified by 2.43 with the Rotax power. Unless you are running where the RPM goes above 5500 I would just let it change, otherwise you will be constantly chasing it.

Agreed.  At some level of turbulence I find I can better compensate (or at least ride out the bumps) by hand than using the AP.  I have a better feel for the throttle changes required when I'm hands-on, and can use stick inputs to lessen the amount of throttle-jockeying required.  Having the AP on kills some of the feedback feel that helps compensate for the changes.

I have had moderate turbulence where the rpm will go from say a 5200rpm setting to 5700rpm or more.  At that point I want to nip that in the bud and make a change.